Golf ball

ABSTRACT

A golf ball ( 1 ) comprises a core ( 3 ) and a cover ( 5 ). The core ( 3 ) has a six-layer structure having first to sixth layers ( 7, 9, 11, 13, 15, 17 ). An inner layer of the core  3  has a low modulus of elasticity. To the contrary, an outer layer of the core ( 3 ) has a high modulus of elasticity. If time series data on force in a z direction which is applied to a load cell provided on a back face of a collision plate inclined by 22 degrees with respect to a horizontal direction when the golf ball ( 1 ) impacts with the collision plate at a speed of 35 m/s in a vertical upward direction are represented by Fn(t), time series data on force in an x direction are represented by Ft(t) and a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by T 1  and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by T 2 , a value of (T 1 /T 2 ) is 1.85 to 2.10. The golf ball ( 1 ) has a great launch angle and generates a low back spin rate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a golf ball and more particularly to an improvement in a trajectory of the golf ball.

[0003] 2. Description of the Related Art

[0004] A golf ball hit with a golf club flies at an upward launch angle with respect to a horizontal direction. The launch angle is caused by a loft angle of a head of the golf club. At the time of launch, the golf ball generates a so-called back spin. The back spin is caused by tangential force generated when the golf ball impacts with the head having the loft angle. It has been reported that the amount of the back spin is almost proportional to an impulse of the tangential force generated during the impact (Dynamics and Design Conference' 98 in Hokkaido, Lecture Articles “Analysis of mechanism of golf ball spinning during impact”.

[0005] A trajectory of the golf ball after the launch is greatly affected by a launch angle and a back spin rate. In other words, the golf ball having a great launch angle tends to have a high trajectory. To the contrary, a golf ball having a small launch angle tends to have a low trajectory. Moreover, a lift is generated on the golf ball through the back spin, so the golf ball having a great back spin rate tends to have a high trajectory and the golf ball having a small back spin rate tends to have a low trajectory.

[0006] A golfer's demand performance for the golf ball includes a flight distance, a hitting feeling, control performance and the like. In particular, in the case in which the golfer uses a long iron, middle iron or wood type golf club (driver, brassie, spoon, baffy, krick or the like), the flight distance is important.

[0007] In order to increase the flight distance when the golf ball is hit with the long iron or the like, it has been well known that the golf ball should have a high trajectory to some extent and a duration of flight should be prolonged. Although the golf ball having a great launch angle or generating a great back spin rate has a high trajectory as described above, a golf ball generating an excessively great back spin rate tends to provide a smaller flight distance. It is supposed that the tendency is caused for the following reasons. More specifically, kinetic energy is consumed by the back spin or force for rearward returning the golf ball is generated by a lift applied vertically to a flight direction up to a maximum trajectory point. It is apparent that a golf ball capable of achieving a high trajectory with a small back spin rate at a high launch angle can provide a great flight distance when it is hit with the long iron or the like.

[0008] Based on such a knowledge, a golf ball generating a smaller back spin rate during hitting and having a great launch angle has been developed in respect of a material and a structure. However, a golfer has highly required a great flight distance. A golf ball to satisfy such a requirement has not been obtained yet.

SUMMARY OF THE INVENTION

[0009] In consideration of such circumstances, it is an object of the present invention to provide a golf ball having a greater launch angle than that of a conventional golf ball during hitting on the same conditions and generating a smaller back spin rate than that of the conventional golf ball.

[0010] In order to achieve the above-mentioned object, the present invention provides a golf ball in which if a direction of a counterclockwise rotation by 22 degrees with respect to a vertical upward direction is set to a z direction, a direction of a counterclockwise rotation by 22 degrees with respect to a horizontal right direction is set to an x direction, time series data on force in the z direction which is applied to a load cell provided on a back face of a collision plate having a surface extended in the x direction when the golf ball impacts with the collision plate at a speed of 35 m/s in the vertical upward direction are represented by Fn(t), time series data on force in the x direction are represented by Ft(t), a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by T1 and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by T2, a value of (T1/T2) is 1.85 to 2.10.

[0011] The golf ball has the value of (T1/T2) greater than that of a conventional golf ball, that is, 1.85 to 2.10. Therefore, an impulse of tangential force is reduced during impact as will be described below in detail. In the golf ball, accordingly, a back spin is less generated (low spin rate) and a great launch angle can be obtained (high launch angle).

[0012] It is preferable that the value of (T1/T2) should be 1.95 to 2.10. It is more preferable that the value of (T1/T2) should be 2.00 to 2.09.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a cross section of a golf ball according to an embodiment of the present invention,

[0014]FIG. 2 is a partial cross section of a device for measuring the value of (T1/T2) of the golf ball illustrated in FIG. 1,

[0015]FIG. 3 is a graph showing an example of Fn(t) and Ft(t) measured by the device illustrated in FIG. 2, and

[0016]FIGS. 4A and 4B are typical views illustrating the relationship between a back spin rate and a launch angle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described below in detail based on a preferred embodiment with reference to the drawings.

[0018]FIG. 1 is a cross section of a golf ball 1 according to an embodiment of the present invention. The golf ball 1 comprises a core 3 and a cover 5. The core 3 includes a first layer 7 which is spherical, a second layer 9 surrounding the first layer 7, a third layer 11 surrounding the second layer 9, a fourth layer 13 surrounding the third layer 11, a fifth layer 15 surrounding the fourth layer 13, and a sixth layer 17 surrounding the fifth layer 15. In other words, the golf ball 1 has a seven-layer structure including the sixth-layer cores 3 and the cover 5. The golf ball 1 is usually provided with a coated layer. The coated layer is not shown in FIG. 1.

[0019] The first to sixth layers (7, 9, 11, 13, 15, 17) are formed by crosslinking a rubber composition. Polybutadiene having high resilience performance is suitably used for a rubber. In particular, it is preferable that high-cis polybutadiene having cis-1, 4 bonding of 90% or more should be used. The polybutadiene may be blended with another rubber such as natural rubber, polyisoprene, a styrene-butadiene copolymer or an ethylene-propylene-diene copolymer. It is preferable that another rubber should be blended in an amount of 50 parts by weight or less based on 100 parts by weight of polybutadiene. In this specification, a numeric value indicated as “part” represents a ratio based on a weight.

[0020] A co-crosslinking agent, organic peroxide and a filler are blended with the rubber composition. Preferable co-crosslinking agent is a metallic salt of α,β-unsaturated carboxylic acid having a carbon number of three to eight. More specifically, a monovalent or bivalent metallic salt of acrylic acid or methacrylic acid is preferable. In particular, zinc acrylate is preferable because the resilience performance of the core 3 can be enhanced. The blending amount of the co-crosslinking agent is regulated so that a modulus of elasticity in each layer is adjusted as will be described below in detail. Consequently, it is possible to obtain the golf ball 1 generating a low spin rate and having a high launch angle.

[0021] Examples of a suitable organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl-cyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide and the like. In particular, the dicumyl peroxide is suitable. The blending amount of the organic peroxide is regulated so that the modulus of elasticity in each layer is adjusted as will be described below in detail. Consequently, it is possible to obtain the golf ball 1 generating a low spin rate and having a high launch angle.

[0022] Examples of the filler include an inorganic filler such as zinc oxide, barium sulfate or calcium carbonate. For example, moreover, a metal filler having a high specific gravity such as tungsten powder or molybdenum powder may be used. In particular, zinc oxide functioning as an activator is preferable. The blending amount of the filler is regulated so that the modulus of elasticity in each layer is adjusted as will be described below in detail. Consequently, it is possible to obtain the golf ball 1 generating a low spin rate and having a high launch angle.

[0023] Furthermore, an additive such as an antioxidant, a peptizer, an organic sulfur compound or rubber powder may be blended in a proper amount with the rubber composition if necessary.

[0024] The core 3 having such layers can be formed by a semi-crosslinking half shell method or a rubber injection method which will be described below in detail.

[0025] The cover 5 is formed of a synthetic resin. A preferable synthetic resin is an ionomer resin. An additive such as a pigment, for example, titanium dioxide, a dispersing agent, an antioxidant, a UV absorber or a light stabilizer may be blended in a proper amount with the cover 5 if necessary. By changing the kind or grade of the synthetic resin to be used for the cover 5, the golf ball 1 generating a low spin rate and having a high launch angle can be obtained as will be described below in detail.

[0026] While the golf ball 1 has a seven-layer structure, the number of layers constituting the golf ball 1 is not restricted thereto. While only an outermost layer is formed of a synthetic resin in the golf ball 1, two outer layers (a so-called two-layer cover) may be formed of the synthetic resin. Furthermore, the number of cover layers may be three or more.

[0027]FIG. 2 is a partial sectional view showing a device for measuring a value of (T1/T2) of the golf ball 1 illustrated in FIG. 1. The device comprises a board 19, a load cell 21, a collision plate 23, a main bolt 25 and a small bolt 27. The collision plate 23 includes a body 29 and a covered plate 31. In FIG. 2, a z direction is obtained by a counterclockwise rotation of 22 degrees with respect to a vertical upward direction. Moreover, an x direction is obtained by a counterclockwise rotation of 22 degrees with respect to a horizontal right direction. α represents 22 degrees to be an angle formed in the horizontal direction and the x direction. The board 19, the load cell 21 and the collision plate 23 are positioned to be extended in the x direction.

[0028] It is preferable that the board 19, the main bolt 25 and the small bolt 27 should be excellent in a strength and a rigidity and should be formed of any material. Usually, steel is used for the material. The board 19 has a thickness of 5.35 mm. Moreover, the main bolt 25 has a type of M10 and the small bolt 27 has a type of M3 based on the JIS.

[0029] A three component force sensor (type 9067) supplied by Kesler Co., Ltd. is used for the load cell 21. The sensor can measure components of force in x, y and z directions. The measurement is carried out through a connection of a charge amplifier (type 5011B supplied by Kesler Co., Ltd.) which is connected to the load cell 21. The load cell 21 has a through hole 33 provided on a center thereof. The main bolt 25 is inserted in the through hole 33.

[0030] The body 29 of the collision plate 23 is formed of stainless steel (SUS-630). The body 29 has a thickness of 15 mm. Moreover, the planar shape of the body 29 is identical to that of the load cell 21 and is a square having a side of 56 mm. The tip of the main bolt 25 is screwed into the body 29. Consequently, the load cell 21 is interposed between the board 19 and the body 29 so that the position of the load cell 21 is fixed.

[0031] The covered plate 31 is fixed to the body 29 with two small bolts 27 and 27. The covered plate 31 is formed of a titanium alloy (6-4Ti) containing 6% by weight of aluminum and 4% by weight of vanadium. The covered plate 31 has a thickness of 2.5 mm. Moreover, the planar shape of the covered plate 31 is identical to that of the load cell 21 and is a square having a side of 56 mm. The covered plate 31 is provided to maintain the state of a collision plane of the collision plate 23 to be constant. The covered plate 31 has a 10 - point mean roughness Rz of 13.6 μm ±2.0 μm.

[0032] When the value of (T1/T2) is to be measured by the device, the golf ball 1 is launched vertically upward and is caused to impact with the collision plate 23. Immediately before the impact, the golf ball 1 has a speed of 35 m/s ±0.3 m/s.

[0033] After the impact, the golf ball 1 rebounds in a lower right direction in FIG. 2. During the impact, the Fn(t) to be time series data on force in the z direction and the Ft(t) to be time series data on force in the x direction are measured by the load cell 21. The measurement is carried out by sampling the data per frequency of 5000000 Hz. The sampled data are subjected to a smoothing processing through the calculation of a moving average for seven points. A time T1 is obtained from the measured Fn(t). The T1 represents a time taken after the start of the impact before the Fn(t) is first changed from a positive number to zero. Moreover, a time T2 is obtained from the measured Ft(t) The T2 represents a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number.

[0034]FIG. 3 is a graph showing an example of the Fn(t) and the Ft(t) measured by the device illustrated in FIG. 2. An origin P0 of the graph is a position where the load cell 21 starts to sense force, and almost corresponds to a time at which the impact of the collision plate 23 with the golf ball 1 is started. The Fn(t) to be force in the z direction is gradually increased from the point P0 and has a maximum value at a point P1, and is then decreased gradually and has a value of zero at a point P2. At the point P2, the load cell 21 starts to sense no force and almost corresponds to a time at which the golf ball 1 goes away from the collision plate 23.

[0035] The Ft(t) to be force in the x direction (so-called tangential force) is gradually increased from the point P0 and has a maximum value at a point P3, and is then decreased gradually and has a negative value after a point P4. After the point P4, the tangential force applied to the golf ball 1 is represented by a curve in a dotted line of FIG. 3. The golf ball 1 goes away from the load cell 21 at the point P2. Therefore, the curve of the Ft(t) sensed by the load cell 21 is turned toward the point P2 and is set to zero thereon. An area Sa represented rightward raised slant lines which is surrounded by the curve of the Ft(t) and a time base represents an impulse having positive tangential force. On the other hand, an area Sb represented leftward raised slant lines which is surrounded by the curve of the Ft(t) and the time base represents an impulse having negative tangential force. Since the impulse Sa is obtained by force applied in the positive direction of an x axis, the force acts in such a direction that a back spin is promoted. On the other hand, since the impulse Sb is obtained by force applied in the negative direction of the x axis, the force acts in such a direction that the back spin is suppressed. As is apparent from FIG. 3, the impulse Sa is much greater than the impulse Sb. A back spin is generated more greatly on the golf ball 1 having a greater value obtained by subtracting the impulse Sb from the impulse Sa.

[0036] The T1 shown in FIG. 3 represents a time taken after the start of the impact before the Fn(t) is first changed from a positive number to zero, that is, a time from the point P0 to the point P2. Moreover, the T2 represents a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number, that is, a time from the point P0 to the point P4.

[0037] The value of (T1/T2) is calculated from the T1 and the T2 thus obtained. In the golf ball 1 shown in FIG. 1, the value of (T1/T2) is 1.85 to 2.10. The value is greater than a value of (T1/T2) of the conventional golf ball, that is, 1.72 to 1.83. In other words, the T2 is much smaller than the T1 in the golf ball 1 shown in FIG. 1. For this reason, the impulse Sa is smaller and the impulse Sb is greater than those in the conventional golf ball. Accordingly, a value obtained by subtracting the impulse Sb from the impulse Sa is very small and a back spin rate is less generated on the golf ball 1.

[0038]FIGS. 4A and 4B are typical views illustrating the relationship between the back spin rate and the launch angle. FIGS. 4A and 4B show a state in which the golf ball 1 is hit with a head 35 of the golf club. The back spin rate is generated greatly on the golf ball 1 shown in FIG. 4A and the back spin rate is less generated on the golf ball 1 shown in FIG. 4B. An arrow E represents a vector of kinetic energy given to the golf ball 1 through hitting and an arrow B represents a vector of energy of a back spin rate. The arrow B in FIG. 4B is shorter than an arrow B in FIG. 4A. Therefore, an angle formed in a horizontal direction by an arrow L to be a composite vector of the arrows E and B is greater in FIG. 4B. This implies that a launch angle is greater in FIG. 4B than that in FIG. 4A. Thus, the golf ball 1 generating a smaller back spin rate tends to have a greater launch angle. The golf ball 1 shown in FIG. 1 has a value of (T1/T2) of 1.85 to 2.10 and a back spin rate is less generated thereon. Therefore, the golf ball 1 also provides a high launch angle.

[0039] If the value of (T1/T2) is less than 1.85, a value obtained by subtracting the impulse Sb from the impulse Sa is increased so that a golf ball neither generates a low spin rate nor has a high launch angle. Moreover, if the value of (T1/T2) is more than 2.10, the curve of the Ft(t) is further changed to be positive before the point P2 so that the impulse to promote the back spin rate is increased. Consequently, the golf ball neither generates a low spin rate nor has a high launch angle. From these viewpoints, the value of (T1/T2) is preferably 1.95 to 2.10, more preferably, 2.00 to 2.09. It is sufficient that the values of the T1 and the T2 can achieve a value of (T1 / T2) of 1.85 to 2.10. Usually, the value of the T1 is 0.6 ms to 0.8 ms and the value of the T2 is 0.3 ms to 0.4 ms.

[0040] The golf ball 1 having the value of (T1/T2) of 1.85 to 2.10 can be obtained by causing the inner layer to have a smaller modulus of elasticity and the outer layer to have a greater modulus of elasticity than those in the conventional golf ball. For example, if a modulus of elasticity in each layer is properly combined within a range shown in the following Table 1 in the golf ball 1 in which the first layer 7 has an outside diameter of 5 mm to 10 mm, each of the second layer 9 to the sixth layer 17 has a thickness of 1.0 mm to 3.0 mm and the cover 5 has a thickness of 1.5 mm to 3.0 mm, a value of (T1/T2) of 1.95 to 2.10 can be achieved. An example of the combination will be described below in detail in the columns of the following examples. TABLE 1 Range of Modulus of Elasticity in Each Layer First layer 20 to 60 MPa Second layer 30 to 70 MPa Third layer 35 to 100 MPa Fourth layer 40 to 140 MPa Fifth layer 70 to 150 MPa Sixth layer 100 to 160 MPa Cover 200 to 400 MPa

[0041] As a matter of course, if a golf ball having a three-layer structure, a four-layer structure, a five-layer structure or a six-layer structure as well as the seven-layer structure includes an inner layer having a smaller modulus of elasticity and an outer layer having a greater modulus of elasticity than those of the conventional golf ball, a value of (T1/T2) of 1.85 to 2.10 can be achieved.

[0042] In this specification, the modulus of elasticity represents a complex modulus of elasticity E* measured in a compression mode by a visco-elasticity spectrometer supplied by Rheology Co., Ltd. The measurement is carried out with an initial strain of 0.4 mm, a displacement amplitude of ±1.5 μm, a frequency of 10 Hz, a starting temperature of −70° C., an ending temperature of 110° C., and a temperature raising speed of 4° C./min. The modulus of elasticity is obtained based on a ratio of amplitudes and a difference in phase between a driving portion and a response portion at a temperature of 20° C. A specimen having a length of 4 mm, a width of 4 mm and a thickness of 2 mm is used for the measurement. The specimen is cut away from the golf ball 1. If the thickness of the layer is too small to cut the specimen away, a slab having a thickness of 2 mm is formed of a polymer composition having the same blending as that of the layer and a specimen is punched out of the slab. In the case in which a layer from which the specimen cannot be cut out is formed of crosslinked rubber, a rubber composition having the same blending as that of the layer is put in a mold including a cavity having a thickness of 2 mm and is crosslinked at a crosslinking temperature of 160° C. for a crosslinking time of 30 minutes so that the slab is obtained. In the case in which the layer from which the specimen cannot be cut out is formed of a synthetic resin composition, a synthetic resin composition having the same blending as that of the layer is injected into the mold including the cavity having a thickness of 2 mm so that the slab is formed.

[0043] The golf ball 1 having a value of (T1/T2) of 1.85 to 2.10 is obtained by setting an outer layer to have a comparatively higher modulus of elasticity and an inner layer to have a comparatively lower modulus of elasticity as described above. In order to obtain the golf ball 1 having such a distribution of the modulus of elasticity, the following means can be used.

[0044] (1) A synthetic resin to be used for the cover 5 has a high rigidity.

[0045] (2) In the core 3, the blending amount of a co-crosslinking agent of the inner layer is decreased and that of the co-crosslinking agent of the outer layer is increased.

[0046] (3) In the core 3, the blending amount of an organic peroxide of the inner layer is decreased and that of the organic peroxide of the outer layer is increased.

[0047] (4) In the core 3, the blending amount of a filler of the inner layer is decreased and that of the filler of the outer layer is increased.

[0048] (5) A filler having a high specific gravity is added to the cover 5.

[0049] (6) A filler having a high specific gravity is added to the outer layer in the core 3.

[0050] (7) A cross linking temperature of the core 3 is regulated to more increase a crosslinking density in the outer layers.

[0051] (8) A thickness of the cover 5 is increased.

[0052] (9) The cover 5 having two or more layers is provided.

[0053] (10) The inner layers of the core 3 are formed of a foam.

EXAMPLES

[0054] Example 1

[0055] 100 parts by weight of high-cis polybutadiene (trade name of “BR01” provided by JSR Co., Ltd.), 18 parts by weight of zinc acrylate, 1.0 part by weight of dicumyl peroxide (trade name of “Percumye D” provided by NOF corporation) and 23.9 parts by weight of zinc oxide were kneaded by means of an internal kneader and a rubber composition was prepared (indicated as J in the following Table 3). The rubber composition was put in a mold including upper and lower parts having hemispherical cavities respectively and was crosslinked for 20 minutes at a temperature of 160 ° C. Consequently, a first layer having a diameter of 6.4 mm was obtained. The first layer had a modulus of elasticity of 44.9 MPa.

[0056] Next, a rubber composition indicated as H in the following Table 3 was put in a mold including a hemispherical cavity having a great inside diameter, and furthermore, an insert core having the same outside diameter as that of the first layer was put therein and the mold was closed. Then, the rubber composition was heated for 20 minutes at a temperature of 160° C. so that a semi-crosslinked half shell was formed. The mold was opened and the insert core was taken out, and the first layer was put in the cavity of the half shell. Furthermore, the mold was closed and the rubber composition was crosslinked for 20 minutes at a temperature of 160° C. Thus, a second layer was formed. The second layer has a thickness of 3.2 mm.

[0057] Each layer was sequentially formed repetitively by such a semi-crosslinking half shell method. Consequently, third to sixth layers having a thickness of 3.2 mm were formed and a core was obtained. A rubber composition indicated as H, a rubber composition indicated as C, the rubber composition indicated as C and a rubber composition indicated as A in the following Table 3 were used for the third to sixth layers, respectively. The type of the rubber composition used in each layer and the modulus of elasticity in each layer are shown in the following Table 2.

[0058] On the other hand, 50 parts by weight of an ionomer resin neutralized with sodium ions (trade name of “Highmilan 1605” provided by Du Pont - Mitsui Polychemicals Company, Ltd.), 50 parts by weight of an ionomer resin neutralized with zinc ions (trade name of “Highmilan 1706” provided by Du Pont —Mitsui Polychemicals Company, Ltd.) and 2 parts by weight of titanium dioxide were blended to prepare a resin composition. Then, a core was put in a mold including upper and lower parts having hemispherical cavities respectively, and the resin composition was injected around the core. Thus, a cover having a thickness of 2.2 mm was formed. The cover had a modulus of elasticity of343.1 MPa. The cover was preprocessed by a conventional method, and furthermore, coating was carried out. Thus, a golf ball according to the example 1 was obtained.

[0059] Examples 2 and 3 and Comparative Examples 1 and 2

[0060] Golf balls according to examples 2 and 3 and comparative examples 1 and 2 were obtained in the same manner as in the example 1 except that a rubber composition for each layer of a core shown in the following Table 2 was used. Each rubber composition is shown in the following Table 3. The type of the rubber composition used for each layer of the golf ball and a modulus of elasticity in each layer are shown in the following Table 2.

[0061] Hitting Test

[0062] 10 golf balls according to each of the examples and the comparative examples were prepared. On the other hand, a No. 4 iron (trade name of “HI-BRID AUTOFOCUS” provided by Sumitomo Rubber Industries, Ltd.) was attached to a swing robot provided by True Temper Co. and the conditions of a machine were adjusted to set a head speed of 38.8 m/s. Then, each golf ball was hit to measure a spin rate obtained immediately after hitting, a launch angle and a flight distance (a distance from a shooting point to a point where the ball is stationary). The following Table 2 shows the result of calculation of a mean value for 10 data in each of the examples and comparative examples. TABLE 2 Result of Evaluation of Golf Ball Comparative Comparative Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 3 Composition- Modulus of (A to L) elasticity (MPa) 1st layer C-119.7 C-119.7 J-44.9  K-42.8  L-40.1  2nd layer C-119.7 C-119.7 H-60.4  I-50.9  L-40.1  3rd layer D-112.3 C-119.7 H-60.4  G-90.0  I-50.9  4th layer D-112.3 C-119.7 C-119.7 B-127.1 I-50.9  5th layer E-104.9 C-119.7 C-119.7 B-127.1 A-134.6 6th layer F-97.4  C-119.7 A-134.6 A-134.6 A-134.6 cover 343.1 343.1 343.1 343.1 343.1 (T1/T2) 1.75 1.84 1.90 2.00 2.09 Spin rate (rpm) 3980 3922 3892 3822 3751 Launch angle 14.1 14.3 14.4 15.1 16.0 (degree) Flight distance 175.7 176.2 176.5 177.6 178.5 (m)

[0063] TABLE 3 Rubber Composition used for Each Layer A B C D E F G H I J K L polybutadiene 100 100 100 100 100 100 100 100 100 100 100 100 zinc acrylate 28.0 27.0 26.5 25.0 23.5 22.0 21.5 20.5 19.0 18.0 17.5 8.0 zinc oxide 20.5 20.6 20.8 21.3 21.9 22.5 22.7 23.0 23.5 23.9 24.0 27.5 Dicumyl peroxide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Modulus of 134.6 127.1 119.7 112.3 104.9 97.4 90.0 60.4 50.9 44.9 42.8 40.1 elasticity (MPa)

[0064] In the Table 2, the golf ball according to each example provides a lower spin rate, a higher launch angle and a greater distance than those of the golf ball according to each comparative example. Based on the result of evaluation, the advantage of the present invention can be confirmed.

[0065] While the present invention has been described in detail by taking a solid golf ball having a multilayered structure as an example, a golf ball comprising a thread winding core can have a flight distance increased if a value of (T1/T2) is 1.85 to 2.10.

[0066] The above description is only illustrative and various changes can be made without departing from the scope of the invention. 

What is claimed is:
 1. A golf ball in which if a direction of a counterclockwise rotation by 22 degrees with respect to a vertical upward direction is set to a z direction, a direction of a counterclockwise rotation by 22 degrees with respect to a horizontal right direction is set to an x direction, time series data on force in the z direction which is applied to a load cell provided on a back face of a collision plate having a surface extended in the x direction when the golf ball impacts with the collision plate at a speed of 35 m/s in the vertical upward direction are represented by Fn(t), time series data on force in the x direction are represented by Ft(t), a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by T1 and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by T2, a value of (T1/T2) is 1.85 to 2.10.
 2. The golf ball according to claim 1, wherein the value of (T1/T2) is 1.95 to 2.10.
 3. The golf ball according to claim 1, wherein the value of (T1/T2) is 2.00 to 2.09. 